Automatic oscillation control



Patented Oct. 31, 195

UNITED STATES PATENT OFFICE 2,527,730 AUTOMATIC OSCILLATION CONTROLRalph H. Hoglund, Bellmore, N. Y., assignor to the United States ofAmerica as represented by the Secretary of War Application March 4,1946, Serial No. 651,936

g 3 Claims. 1

This invention relates generally to electrical apparatus and moreparticularly to means for automatically adjusting electron tube circuitparameters to obtain optimum operating conditions.

In certain oscillators where an ultra high radio frequency signal is tobe generated use is made of a velocity-modulated vacuum tube of thereflex type. For a tube of this type to oscillate at a particularfrequency whereby it furnishes maximum power output it is required thata critical voltage be applied to the reflector anode of the tube.Frequently the supply voltage for the reflector anode changes whiletheoscillator is in operation and sometimes when the oscillator is shut offfor a while and then restarted. In certain applications where thereflector anode adjustment is not readily accessible, it may not bepractical-to depend on manual adjustment of the reflector anode voltage.In addition the operator may not be skilled in adjusting the reflectoranode voltage properly. Accordingly, one object of the present inventionis to provide a means whereby the voltage applied to the reiiector anodeof such a v-m tube is adjusted autoreflex velocity-modulated oscillatortube l0, hereinafter referred to simply as the v-m tube I0. V-m tube I0includes a cathode II, control grid I2, cavity l3 and reflector anodeI4. Cavity I3, which is represented in cross-section, includes twoparallel grids I5 placed at right angles to the direction of flow ofelectrons through the tube. Customarily cavity I3 is grounded.

Battery I6 is connected between cavity I3 and cathode II, its positiveterminal being connected to cavity I3. Electrons leaving cathode II arethus accelerated towards the cavity grids l5 by virtue of this positivepotential existing between the two elements. A second battery I! isconnected between control grid I2 and cathode II, its positive terminalbeing connected to control grid I2. Control grid l2 regulates the totalnum- 2 her of electrons traversing between cathode II and cavity gridsI5. The output power is taken from cavity I3 by means of a probe I8projecting therein and leading to the external circuit through a coaxialline I9.

Reflector anode I4 is connected to the variable ,tap of a potentiometer20. The ends 2I and 22 of potentiometer 20 are connected to the ends Eland 32, respectively, of the secondary winding 33 of a transformer 30.End 22 of potentiometer 20 is connected also to the variable tap 24 .ofa potentiometer 23. The position of the variable tap 24 is governed bythe angular displacement of a permanent-magnet (p-m) motor 26. P-m motor26 has two input terminals 21 and 28. A battery 25 is connected acrossthe potentiometer 23, the positive terminal of this battery beinggrounded. Battery 25 effectively supplies to reflector anode [4 anegative voltage with respect to cavity I3.

A portion of the output of the v-m tube III is taken from the coaxialoutput line I9 and applied to a crystal detector 40. By-pass condenser4! is connected from one end of crystal to ground.

Signals which appear in the crystal detector output are separated intoalternating current (A.-C.) and direct current (D.-C.) components. TheA.-C. component is amplified by a suitable audio frequency amplifier 42and applied through a coupling network consisting of coupling condenser43, grid resistor 44 and bias battery 45 to control grids 5i and 6! ofvacuum tubes and 60, respectively. The potential from bias battery 45 issufficient to render vacuum tubes 50 and nonconductive when no signal isapplied to the control grids.

The D.-C. component of crystal current output is amplified by a suitableD.-C. amplifier 46 and applied to winding II of a D.C. relay I0.

Anodes 52 and 62 of vacuum tubes 50 and 60, respectively, are connectedto the ends of centertapped secondary winding 34 of transformer30. Thecenter tap of secondary winding 34'is at ground potential. To primarywinding 35 of transformer 30 is applied a suitable alternating voltage.

Cathodes 53 and 63 of vacuum tubes 50 and 60,

respectively, are connected to windings 8| and to the negative terminalof battery 14. D.-C. relay I includes make-and-break fixed contacts I6and 17 associated with movable contact 13. Relay It also includesmake-and-break fixed contacts I8 and I9 associated with movable contactI5. When the relay is deenergized, movable contacts l3 and are incontact with fixed contacts 16 and 18, respectively.

Relay 80 includes make-and-break fixed contacts 83 and 82 associatedwith movable contact 84, and make-and-break fixed contacts 85 and 86associated with movable contact 81. When reversing relay 8!] isdeenergized, movable contacts 84 and 8! are in contact with fixedcontacts 82 and 85, respectively.

Reversing relay 98 includes a movable contact 92 and a fixed contact 93.When reversing relay 9D is energized movable contact 92 is in contactwith fixed contact 93.

Fixed contact 93 of reversing relay 9 is connected to terminal 21 of p-mmotor 26, to fixed contact I9 of D.-C. relay 7!] and to fixed contact 86of reversing relay 89. Movable contact 92 of reversing relay 90 isconnected to fixed contact 82 of reversing relay 80.

Fixed contact 83 of reversing relay 8B is connected to fixed contact 85of reversing relay 89, to terminal 28 of p-m motor 25, and to fixedcontact ll of D.-C. relay l0. Movable contacts 84 and 87 of reversingrelay 80 are connected to fixed contacts I6 and "I8, respectively, ofD.-C. relay H3.

The interconnections between the relays described above are such thatwhen D.-C. relay it and reversing relay 90 are deenergizd and reversingrelay 80 is energized, a voltage is applied to motor 26 to drive it in aforward direction. When relays ID and 86 are deenergized and reversingrelay 9D is energized, a voltage will be supplied to the motor 26 tocause it to rotate in a reverse direction. When D.-C. relay 19 isenergized, the motor 26 will be driven in a forward direction regardlessof the position of the other relays.

Operation of this circuit will be described first assuming that thereflector anode voltage is adjusted so that oscillations in the v-m tubeII) are not possible. Lack of oscillation will result in zero D.-C.output from the crystal detector 40. The D.-C. amplifier 46 and D.-C.relay 10 are arranged in such a manner that relay ID will be energized.This effectively connects battery It directly to motor 28 and causes thelatter to rotate in a forward direction. Variable tap 24 01potentiometer 23 is thereby moved and the voltage applied to thereflector anode I4 is changed accordingly. Potentiometer 23 is soconstructed that variable tap 24 will rotate continuously through 360degrees. Hence, a voltage will be reached which will allow theoscillator to become operative and supply power to the crystal detector.When such a condition occurs, D.-C. relay I0 is deenergized, the sourceof potential to the motor is interrupted, and the remainder of thecircuit is allowed to come into operation.

When oscillations begin, the output is modulated by the small-amplitudeA.-C. signal which is induced in secondary winding 33 and applied toreflector anode I 4. The effects of the modulating voltage on the outputof the oscillator is more clearly shown in Fig. 2. In Fig. 2 the power,as

measured by D.-C. crystal current, is plotted against the reflectoranode voltage. The power output curve is a. resonance type curve withmaximum power occurring for a reflector anode volt age of approximatelyE0 volts. It is desirable that the reflector voltage be adjusted to theoptimum value of E0 volts.

The operation of the circuit will next be explained when the reflectoranode voltage, E1, is a value greater than the optimum value, E0 voltsas indicated in Fig. 2. In Fig. 2 the sinusoidal A.-C. modulatingvoltage IOI has been shown superimposed upon the reflector anode voltageE1. The resultant power output variation (indicated by the crystalcurrent) is shown by the sinusoidal error signal curve I02.

The error signal I02 is amplified in audio amplifier 42 and applied tothe control grids of vacuum tubes 50 and 60. As mentioned beforehand thebias voltage also applied to the control grids prevents either tube fromconducting when the error signal is absent or of low amplitude. Thevacuum tubes 50 and 60 together function as a phase detector, giving afirst output when the error signal is of one phase and a second outputwhen of the opposite phase in a manner to be described.

A sinusoidal alternating reference voltage of the same frequenc as theerror signal I02 is applied to the anodes of vacuum tubes 59 and fromsecondary winding 34 of transformer 30. Since secondary winding 34 iscenter-tapped to ground the application of the sinusoidal alternatingvoltage to the plates of vacuum tubes 50 and 60 will result in voltageson these plates which are out of phase with each other. It will beassumed that for the first half-cycle of the error signal I02 thecontrol grids of the vacuum tubes 50 and 60 are driven above cutoff, andfurthermore, that the polarity of the reference signal on plate 52 ispositive while that on plate 62 is negative. Under these conditionsvacuum tube 50 will conduct and vacuum tube 88 will not conduct. On theother half-cycle of the error signal I02 the polarity of the signal onplate 62 will be positive and that on plate 52 negative. However,reference to Fig. 2 will show that the error signal I02 on the controlgrids now drives the grids below cut off. Therefore vacuum tube 50 willnot conduct during either half-cycle for an error signal of the phaseshown.

Reversing relay 80 i thus energized when tube 50 conducts and motor 26is caused to rotate in a forward direction. The sense of the rotation issuch as to alter the setting on potentiometer 23 so that the reflectoranode voltage is decreased.

It should be evident to those skilled in the art that if the reflectoranode voltage had been less than the optimum value E0 volts, the errorsignal would have been reversed in phase, vacuum tube 60 of the phasedetector would have conducted a current, relay 98 would have beenenergized, motor 25 would have rotated in a reverse direction, and thereflector anode voltage would have been increased accordingly.

As a result of this action the presence of an error signal from thecrystal detector 40 will cause one of the vacuum tubes in the phasedetector to conduct, and a difference of 180 degrees in phase willselect which tube will conduct and hence which relay will operate.

When the reflector anode voltage reaches the proper value E0, the errorsignal will be substantially of low amplitude, negative pulses as shownby curve I03 in Fig. 2. When the error signal is as shown by curve I03,neither tube 50 nor 60 of the phase detector will conduct, since neithergrid is driven above cut off. Both reversing relays 80 and remaindeenergized, motor 26 does not rotate, and the reflector anode voltageis left at the optimum value of E0 volts.

The foregoing has shown that the presence of the error signalautomatically selects the proper direction for the variable tap onpotentiometer 23 to travel to obtain optimum reflector anode voltage. Itis only necessary for relay 80 and 90 in the plate circuits of the twophase detector vacuum tubes 50 and 60 to reverse the motor 26 in such amanner that it will adjust the reflector anode voltage in the properdirection. The circuit also provides for automatically adjusting thereflector anode voltage so that oscillations are possible.

It should be evident that the device herein disclosed may be adapted tocontrol the operation of any specific device having a similarcurrentvoltage characteristic.

While there has been described hereinabove what is at present consideredto be a preferred embodiment of this invention, it will be obvious tothose skilled in the art that various changes and modifications may bemade therein without departing from the scope of the invention as setforth in the appended claims.

What is claimed is:

1. In combination with a reflex velocity-modulated vacuum tube includingat least a reflector anode and a cavity, means for causing saidvelocity-modulated tube to oscillate and produce a radio frequencysignal, means for modulating said radio frequency signal in a periodicmanner, means for extracting the modulated radio frequency power fromsaid cavity and producing therefrom a rectified direct-current componentand an error signal alternating-current component proportional to saidradio frequency power, a potentiometer, a motor acting in conjunctionwith said potentiometer for adjusting the value of direct voltageapplied to said reflector anode, means responsive to the direct-currentcomponent in the output of said vacuum tube for energizing said motorwhen said direct-current component is zero, selective means for causingsaid motor to operate in a first direction when said error signal is ofa first phase relative to the output of said modulating means, and otherselective means for causing said motor to operate in a second directionwhen said a-c component of error signal is of a second phase relative tothe output of said modulating means.

2. In combination with a vacuum tube oscillator for producing in itsoutput a radio frequency signal and having at least a cavity and areflector anode, means for modulating said radio frequency signal toproduce a modulated radio frequency output signal, means for extractinga directcurrent component and an alternating-current component from saidmodulated output signal, regulating means for adjusting the directvoltage applied to said reflector anode, means responsive to said directvoltage for actuating said regulating means to maintain said vacuum tubein a state of oscillation, and selective means sensitive to the phase ofsaid alternating-current component relative to the output of saidmodulating means for causing said regulating means to operate inalternative directions depending upon such phase, to maintain the vacuumtube in a condition of maximum oscillation.

3. In combination with a radio frequency vacuum tube oscillator havingat least a cavity and a reflector anode, the output frequency of saidoscillator varying with the voltage applied at said anode and the outputvoltage reaching a maximum at the resonant frequency of said vacuumtube, direct current means for varying the voltage of the reflectoranode, alternating current means in series with said direct currentmeans for modulating the anode voltage and consequently the frequency ofsaid oscillator, rectifier means responsive to the output of saidoscillator for obtaining a direct voltage output proportional to theaverage oscillator output voltage and an alternating voltage outputresulting from the modulation, means responsive to said direct voltageoutput for adjusting said reflector anode voltage to initiate ormaintain oscillation and means responsive to the phase of saidalternating voltage output component with respect to the phase of saidmodulating means to maintain the oscillations at maximum.

RALPH H. HOGLUND.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,294,942 Varian et al Sept. 8,1942 2,337,214 Tunick Dec. 21, 1943 2,367,868 Jones Jan. 23, 19452,404,568 Dow July 23, 1946 2,444,349 Harrison June 29, 1948

